In the paper making art with the use of a conventional fourdrinier fabric, a slurry of paper material is supplied to a travelling endless fabric for paper making, on which fabric cellulose fiber is isolated from the slurry to form a wet paper web. The fabric for paper making thus works as a filter for forming a wet paper web. A mesh orifice, referred to also as a drain pore, of the fabric performs a function in isolating water from the slurry. In a fourdrinier paper making machine, the fabric for paper making also works as a driving belt with tension in the machine direction being applied to it, so that it is necessary for the fabric to have stability of its attitude.
There are some problems in the paper making art, particularly in fabrics for paper making, which have the following requirements: high retention of the paper material, i.e. little loss of the raw material being washed away from the paper making surface of the fabric, no generation of wire marks, good drainage capability and low water carrying property, high abrasion resistance, and high stability of attitude.
For the purpose of filling the aforementioned requirements for the fabric for paper making, a variety of proposals have hitherto been made. However, at present none of them have been found satisfactory to meet the above requirements.
For example, a finely woven fabric for paper making which is made of a fine thread in order to prevent the wire marks is deficient in the stability of attitude and has low abrasion resistance. The formation of paper making surfaces with wefts has recently been attempted in order to improve the retention of the paper material. When the paper making surface is formed with wefts, paper material will not directly stop up the drain pores which are present between warps and thus has an effect for improving the draining ability of the fabric. On the other hand, such a paper making surface has a large gap between wefts, so that it has a problem of increasing wire marks.
It has been also proposed that, in a double layer fabric wherein the paper making surface is formed with more wefts that warps, to increase the weft threads on the paper making surface by arranging floats, the so-called floating yarns, as the weft threads. The floating yarns are fine threads not being woven into a weave in the form of interweave of warps and wefts like the usual fabric. This proposal is an interesting technical idea from the viewpoint of increasing the weft threads of the paper making surface. However, this method cannot be said to be practical in actual conditions of paper making. In other words, the weft threads which have not been woven into warp threads are exactly the floating yarns, so that they tend to be displaced and collected together under the fluid pressure applied thereto during the supply of a slurry to the paper making fabric. The result is that the paper making surface cannot be maintained flat or uniform. Accordingly, this method is only of interest as an idea and suffers problems in practical use.
The problem of the wire marks is distinguished particularly in the case of a single layer fabric in which weft yarns form projections on the paper making surface.
Another proposal for the use of a multiple layer fabric has also been made in order to maintain the drainage ability, to make the paper making surface with the fine mesh size and to ensure the surface abrasion resistance.
Recently, the operating speed of a paper making machine has been extensively increased for improving the efficiency of manufacturing paper, which gives rise to another problem. The multiple layer fabric takes advantageous effects, which have not been accomplished by a single layer fabric; it has a large three-dimensional space because of its structure and thus has a high water carrying property. Therefore, if it rotates at a high speed, water retained in the endless fabric is scattered at the turning and rotating part of the paper machine.
On the other hand, a single layer fabric has a low water carrying property, so that no problem as described above will be caused. The single layer, however, has problems that it tends to bring about wire marks as described above and is poor in the retention of paper material and thus in the yield of producing paper.